A laser driver circuit is used for modulating the light output of a laser diode at high frequencies in accordance with data applied to the driver circuit. The laser driver circuit is usually based on a balanced differential pair with a differential data input being applied to the differential pair.
However, various features associated with laser driver circuits lead to resonances which are problematic. For example, the impedance mismatch between the laser driver output and a laser, especially coupled with reactive elements between them, can cause resonances. Resonances modify signals within a circuit, and may distort the output signal of the laser.
In order to attempt to overcome the resonance problems, several methods are employed by prior art devices. For example, it is known to use resistors in series to attempt to dampen the resonances, but passive resistive components are lossy and often cannot be used due to limited voltage headroom in the laser driver circuit. Alternatively, it is known to use reactive components or tuning stubs to match input and output impedances and reduce the resonances, but the reactive components or tuning stubs must be of a very high quality, which increases the cost of manufacture, and finely tuned, which limits the range of operating frequencies.
Therefore, it is desirable to remove, or at least reduce, resonances in a driver circuit without adversely affecting the output of the driver circuit.